Thermo-chemically activated intramedullary bone stent

ABSTRACT

The present invention provides a bone fixation device for implantation into the intramedullary canal of a bone. The bone fixation device may include a support structure and a thermo-chemically activated matrix. The support structure may be radially expandable and contractible, and sufficiently flexible to be inserted into the intramedullary canal through an opening which is not parallel to the intramedullary canal. The matrix may attain a first thermo-chemical state via the addition of energy, and a second thermo-chemical state via the dissipation of energy. While in the first thermo-chemical state, the matrix is deformable and can conform to a shape matching the contours of the intramedullary canal of the bone. As the matrix attains the second thermo-chemical state, it may crystallize and becomes relatively hardened. An implant deformation apparatus may be used to expand the device within the intramedullary canal. The device may include a series of nested telescoping components.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of the following, which isincorporated herein by reference:

Pending prior U.S. Provisional Patent Application No. 60/913,696, filedApr. 24, 2007, which carries Applicants' docket no. OST-1 PROV, and isentitled THERMO-CHEMICALLY ACTIVATED INTRAMEDULLARY BONE STENT.

BACKGROUND OF THE INVENTION

1. The Field of the Invention

The present invention relates generally to orthopedic devices for thesurgical treatment of bone fractures and, more particularly, to thefixation and stabilization of fracture sites with an intramedullarydevice that is deformable and conforms to the shape of theintramedullary canal.

2. The Relevant Technology

Orthopedic medicine provides a wide array of implants that can beattached to bone to repair fractures. External fixation involves theattachment of a device that protrudes out of the skin, and thereforecarries significant risk of infection. May fractures in long bones canbe repaired through the use of bone plates, which are implanted andattached to lie directly on the bone surface. The bone plate thenremains in the body long enough to allow the fractured bone to healproperly. Unfortunately, such bone plates often require the surgicalexposure of substantially the entire length of bone to which the plateis to be attached. Such exposure typically results in a lengthy andpainful healing process, which must often be repeated when theimplantation site is again exposed to allow removal of the plate. Thereis a need in the art for implants and related instruments that do notrequire such broad exposure of the fractured bone, while minimizing theprobability of infection by avoiding elements that must protrude throughthe skin as the bone heals.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the present invention will now be discussed withreference to the appended drawings. It is appreciated that thesedrawings depict only typical embodiments of the invention and aretherefore not to be considered limiting of its scope. The drawings maynot be to scale.

FIG. 1 is a perspective view of an intramedullary bone fixation deviceaccording to one embodiment of the invention, comprising a supportstructure which includes a cage and a plurality of rods, and athermo-chemically activated thermoplastic matrix;

FIG. 2 is a perspective view of the cage of FIG. 1;

FIGS. 3A-3I are perspective views of various embodiments of stentportions suitable for incorporation into the support structure of FIG.2;

FIG. 4 is an enlarged perspective view of a first end of the cage ofFIG. 2;

FIG. 5 is a perspective view of the rods of FIG. 1;

FIG. 6 is a perspective view of the thermoplastic matrix of FIG. 1;

FIG. 7 is a longitudinal cross-sectional view of a bone with analternative embodiment of an intramedullary bone fixation devicepartially inserted into the intramedullary canal;

FIG. 8 is a longitudinal cross-sectional view of a bone with theintramedullary bone fixation device of FIG. 7 implanted inside a secondintramedullary bone fixation device;

FIG. 9A is an enlarged cross-sectional view of one section of the boneand intramedullary bone fixation devices of FIG. 8;

FIG. 9B is an enlarged cross-sectional view of another section of thebone and intramedullary bone fixation devices of FIG. 8;

FIG. 9C is an enlarged cross-sectional view of another section of thebone and intramedullary bone fixation devices of FIG. 8;

FIG. 10 is a perspective cutaway view of an alternative embodiment of anintramedullary bone fixation device comprising a cage, rods, sutures anda thermoplastic matrix;

FIGS. 11A-11E are cross-sectional views of the intramedullary bonefixation device of FIG. 10, illustrating radial expansion of the devicefrom a contracted state in FIG. 11A to a fully expanded state in FIG.11E.

FIGS. 12A-12E are cross-sectional views of an alternative embodiment ofan intramedullary bone fixation device, illustrating radial expansion ofthe device from a contracted state in FIG. 12A to a fully expanded statein FIG. 12E.

FIG. 13A is a perspective view of a support structure in a contractedstate according to one alternative embodiment of the invention;

FIG. 13B is a perspective view of the support structure of FIG. 13A inan expanded state;

FIG. 14A is a perspective view of a cage in a contracted state;

FIG. 14B is an end view of the cage of 14A in a contracted state;

FIG. 14C is a perspective view of a cage in an expanded state;

FIG. 14D is an end view of the cage of 14C in an expanded state;

FIG. 15 is a perspective view of a slotted support structure;

FIG. 16A is a perspective view of a shaft portion of a mechanicalexpansion apparatus suitable for use with the device of FIG. 1;

FIG. 16B is a perspective view of the complete mechanical expansionapparatus of FIG. 16A;

FIG. 17 is a longitudinal cross-sectional view of a bone with anintramedullary bone fixation device in a contracted state and a balloonexpansion apparatus in the intramedullary canal of the bone, and aregulator apparatus;

FIG. 18 is a longitudinal cross-sectional view of a portion of the boneof FIG. 17, with the intramedullary bone fixation device in a contractedstate and a balloon expansion apparatus of FIG. 17;

FIG. 19 is a longitudinal cross-sectional view of the bone,intramedullary bone fixation device and balloon expansion apparatus ofFIG. 17, with the balloon in an inflated state and the intramedullarybone fixation device in an expanded state;

FIG. 20A is an enlarged cross-sectional view of one section of the boneand intramedullary bone fixation device of FIG. 19;

FIG. 20B is an enlarged cross-sectional view of another section of thebone and intramedullary bone fixation device of FIG. 19;

FIG. 20C is an enlarged cross-sectional view of another section of thebone and intramedullary bone fixation device of FIG. 19;

FIG. 21 is a longitudinal cross-sectional view of the bone,intramedullary bone fixation device and balloon expansion apparatus ofFIG. 17, with the balloon in a deflated state and the and intramedullarybone fixation device in an expanded state, with the balloon expansionapparatus partially removed from the intramedullary bone fixationdevice;

FIG. 22A is a perspective view of a telescoping bone fixation device inan extended state according to one alternative embodiment of theinvention;

FIG. 22B is a longitudinal cross-sectional view of a connection betweentwo nesting components of the telescoping bone fixation device of FIG.22A;

FIG. 23 is a perspective view of a telescoping bone fixation device withmesh-like components and a thermoplastic matrix according to anotheralternative embodiment of the invention, in an extended state;

FIG. 24 is a perspective view of a helically threaded telescoping bonefixation device according to yet another alternative embodiment of theinvention, in a partially extended state;

FIG. 25A is a perspective view of one nesting component of the helicallythreaded telescoping bone fixation device of FIG. 24; and

FIG. 25B is a perspective view of another nesting component of thehelically threaded telescoping bone fixation device of FIG. 24.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, a perspective view illustrates an embodiment of anintramedullary bone fixation composite device 10. The composite device10 comprises a support structure II and a thermo-chemically activatedthermoplastic matrix 16. The support structure 11 comprises a cage 12,and at least one stiffening rod 14. The composite device 10 is generallytubular in form and has a longitudinal axis 24 and a transverse axis 26.A hollow central core 18 extends the length of the device 10, surroundedby the cage 12 and rods 14, which are embedded in the thermoplasticmatrix 16. An outer perimeter 22 bounds the outer surface of thecomposite device 10. The composite device 10 is an implant which is ableto transition from a contracted and flexible state for introduction intothe intramedullary canal, to an expanded and hardened state providingrigid support and alignment for fixation of the surrounding bone, onceimplanted and allowed to expand to the perimeter of the canal. Thethermoplasticity of the matrix 16 allows the composite device 10 toconform to the shape of the surrounding intramedullary canal at a firststate, and harden in its conformed shape at a second state providingtorsional, axial, and bending reinforcement of the bone fragments duringbone healing. When contracted for insertion (or removal), a diameter 20along the transverse axis 26 of the device is reduced, and the lengthalong the longitudinal axis 24 of the device may be constant orincreased. When expanded within the intramedullary canal, the diameter20 is increased, and the length may be constant or decreased.

As seen in FIG. 2, the cage 12 is an elongated, generally web-like tubewhich allows radial expansion and contraction over at least part andpreferably all of its length, and bending flexibility as bending loadsare applied. The cage 12 has a first end 30, a second end 32 and asleeve 34 which extends between the ends. The sleeve 34 has anattachment portion 36 and a web-like stent portion 38. The cage ishollow and generally circular in cross-sectional shape, although theweb-like construction allows the cross-sectional shape to vary toconform to the contours of the surrounding intramedullary canal. Theshape of the intramedullary canal varies along its length, and itscross-sectional shape may be substantially circular, generallytriangular or another shape. The cage 12 may comprise a tubular woven orbraided cage, a laser cut tubing cage, a machined cage, or a chemicallyetched tubing cage made from materials such as Nitinol, stainless steel,Co—Cr, Titanium alloys, Tantalum, plastic, polymer or otherbiocompatible materials, among others. In the embodiment depicted, thestent portion 38 comprises a majority of the sleeve 34. However, inother embodiments the stent portion may be a smaller proportion of thesleeve, or comprise the entire sleeve. Attachment portions 36 may belocated at one, both, or neither of the ends of the sleeve, orintermittently along the sleeve length.

Referring to FIG. 3, possible configurations of the web-like structureof the stent portion 38 are shown, comprising examples of commerciallyavailable stent shapes. These figures show the approximate pattern ofthe web-like structure. These patterns are adaptable to a variety oflengths, diameters, density of repeatable patterns, wire thicknesses,web areas, and other structural characteristics such that the generalstent shape can be configured to a particular bone morphology and size.FIG. 3A is representative of a Johnson and Johnson Palmaz-Schatz™Version 2 stent. FIG. 3B represents a Medtronic Wiktor™ stent. FIG. 3Crepresents the general shape of a Schneider “Magic” Wallstent™ stent.FIG. 3D represents a Scimed NIR™ stent. FIG. 3E represents an ArterialVascular Engineering (AVE™) Microstent. FIG. 3F is representative of aBiotronik Stent™. FIG. 3G is meant to represent the general shape andconstruct of a Johnson and Johnson Palmaz-Schatz™ stent. FIG. 3Hrepresents a Global Therapeutics Freedom™ stent. FIG. 3I is drawn torepresent the adaptable structure of a Scimed Radius™ stent which likeall the previously presented representative figures can be configured tothe length, diameter and size needed to conform to the intramedullaryshape of a particular bone. The stent portion may also be configuredwith more than one pattern along its length or diameter if needed tobetter conform to the desired geometry. The stent portion need not be acommercially available stent; it may also have a unique configurationwhich is constructed from wire, woven, machined, laser cut, orchemically etched.

FIG. 4 is an enlarged view of the first end 30, the attachment portion36 and part of the stent portion 38 of the cage 12. The attachmentportion 36 comprises struts 40 which extend from the stent portion 38and terminate at loops 42, which allow for the attachment of instrumentsfor device placement, adjustment and removal. Other fasteners such asholes or hooks, among others, may be used instead of loops. Between thestruts 40 at the first end 30, linkages 44 connect each strut to theadjacent strut. The linkages allow for radial and longitudinalcontraction and expansion of the struts 40 and therefore the first end30, as the device is contracted and expanded during implantation andremoval. The web-like configuration of the stent portion 38 allows forradial and longitudinal contraction and expansion of the remainder ofthe cage 12.

Referring to FIG. 5, at least one, and optionally, a plurality, ofstiffening rods 14 are oriented parallel to the longitudinal axis of thecage 12 and are contained by the cage in such a way as to allow thestiffening rod(s) to move radially with the cage as the cage contractsand expands. Each rod 14 has a first end 50, a second end 52 and a shaft56. Each rod 14 may have loops, holes, hooks or other attachmentstructures at the second end 52 to connect to second end of cage 12. Therods 14 may be threaded loosely or otherwise linked into the stentportion 38 of the cage 12. Holes (not shown) may extend transverselythrough the rods, and individual webs of the stent portion may passthrough the holes to retain the rods. The rods 14 may extend the fulllength of the cage 12, or preferably from the second end 32 of the cageto the upper end of the stent portion 38. The stiffening rods 14 can bemade from any biocompatible material such as stainless steel, cobaltchromium alloys, tantalum, zirconium alloys, titanium or titaniumalloys, particularly beta titanium alloys. The stiffening rods 14 canalso be made from non-metal biocompatible materials such as PEEK,Acetal, bioabsorbable materials, ceramics and biocomposites. Eachstiffening rod 14 is sufficiently flexible to temporarily bend as thedevice (in a contracted state) is introduced into the intramedullarycanal. Additionally, the rods may be knurled, threaded or otherwisetreated to provide adhesion and interdigitation of the matrix and cage.Once the device 10 is inserted and expanded radially, the rods 14 arealigned parallel to the longitudinal axis of the bone and line the innersurface of the canal, within the cage and matrix of the device.

The ratio of longitudinal contraction to radial expansion of thecomposite device 10 varies depending upon the configuration of the stentportion of the cage, the length of the linkages, and the length andplacement of the rods. Some embodiments have a low ratio, in which asmall decrease in the length of the cage results in a large increase inthe radial expansion (as measured by change in the core diameter 20).Other embodiments have a 1:1 ratio (a contraction in cage length resultsin an equal measurement of radial expansion), or a higher ratio, inwhich a large decrease in longitudinal contraction produces a smallincrease in radial expansion. The choice of embodiment will depend uponfactors such as the length and diameter of the particular bone to befixed, accessibility to the bone, and severity of the fracture, amongothers.

Referring to FIG. 6, the thermoplastic matrix 16 may bethermo-chemically activated, and may surround the support structure 11of FIG. 2, or the support structure of any of the embodiments describedbelow. The matrix 16 comprises a material which has physical propertiesthat change between a first and second state. For example, the materialmay be flexible and deformable at a first state and hard and more rigidat a second state. This can be accomplished by changing factors such asthe molecular structure of chemical components of the matrix 16 from onestate to another. Methods of changing the molecular structure of amaterial, and thus the physical properties of the material, includechanging the temperature of the material, exposing the material to gammaradiation and altering the crosslinking bonds between molecular chainsin the material, exposing the material to ultraviolet radiation causingthe material to cure and harden, exposing the material to a secondmaterial allowing cross-linking and molecular bonding, allowing thematerial to harden over time by increasing the crystallinity within themolecular structure, and other methods that alter the bonding betweenthe molecules in the matrix 16 material and correspondingly alter itsmaterial properties.

The matrix 16 may comprise a thermoplastic biocompatible polymer orpolymer blend comprising polymers such as polylactic acid (PLA), polyε-caprolactone (PCL), trimethylene carbonate (TMC), polyglycolic acid(PGA), poly l-lactic acid (PLLA), poly d-l-lactide (PDLLA),poly-D,L-lactic acid-polyethyleneglycol (PLA-PEG) or other biocompatiblepolymers. Each of these polymers has a glass transition temperatureT_(g) such that when raised to a temperature above its T_(g), thepolymer is rubbery, flexible and deformable. When lowered to atemperature below its T_(g), the polymer is crystallized andsubstantially rigid. Each of these polymers or blends is capable ofbeing transformed by the application of energy to a firstthermo-chemical state, in which it is at a temperature above its glasstransition temperature T_(g). When, through dissipation of energy, thetemperature is reduced to below T_(g), the polymer or blend is at asecond thermo-chemical state. These thermoplastic properties of thepolymers allow them to be repetitively heated to above T_(g), andsubsequently cooled to below T_(g), moving repeatedly between the firstand second thermo-chemical states.

Preferred polymers have a glass transition temperature T_(g) that isabove body temperature, but below the temperature known to cause thermalnecrosis of tissues. A preferred blend is crystallized and substantiallyrigid at human body temperature, and has a T_(g) which ranges from about10° C. above body temperature to about 35° C. above body temperature.This acceptable T_(g) range is between about 50° C. and about 80° C.,and preferably between about 55° and about 65° C. Preferably, thethermoplastic matrix 16 comprises a blend of polymers such as PCL andPLA, or PCL and PGA. Table 1 displays the melting points (T_(m)), glasstransition temperatures (T_(g)) and thermal decomposition temperatures(T_(dec)) of selected synthetic absorable polymers.

TABLE 1 Melting, glass transition and thermal decomposition temperaturesof selected synthetic absorbable polymers. Polymer T_(m) (° C.) T_(g) (°C.) T_(dec) (° C.) PGA 230 36 260 PLLA 170 56 240 PLA — 57 — PCL 60 −62— Polyglactin910 200 40 250 Polydioxanone 106 <20 190 Polyglyconate 213<20 260

Additional biocompatible polymers which may be included in the matrix16, individually or in a blend, comprise aliphatic polyesters includingpolyglycolide, poly(dl-lactide), poly(l-lactide), poly(δ-valerolactone),polyhydroxybutyrate; polyanhydrides includingpoly[bis(p-carboxyphenoxy)propane anhydride], poly(carboxy phenoxyaceticacid), poly(carboxy pheoxyvaleric acid); polyphosphazenes includingaryloxyphosphazene polymer and amino acid esters; poly (ortho esters);poly(p-dioxane); poly(amino acids) including poly(glutamicacid-co-glutamate); erodable hydrogels; and natural polymers includingcollagen (protein) and chitosan (polysaccharide).

The thermoplastic matrix 16 may further include at least one bioactivematerial to promote growth of bone material and accelerate healing offractures. These bioactive materials include but are not limited tohydroxylapatite, tetracalcium phosphate, β-tricalcium phosphate,fluorapatite, magnesium whitlockite, β-whitlockite, apatite/wollastoniteglass ceramic, calcium phosphate particle reinforced polyethylene,bioactive glasses, bioactive glass ceramics, polycrystalline glassceramics, and polyethylene hydroxylapatite.

The support structure 11 may be embedded in the thermoplastic matrix 16through insert molding, pulltrusion, by dipping the support structureinto the thermoplastic matrix material while it is at a temperatureabove T_(g), or by other coating methods. A variety of different methodsmay alternatively be used to assemble the thermoplastic matrix 16 andthe support structure 11.

Referring to FIG. 7, a longitudinal cross-section of a bone illustratesimplantation of an intramedullary bone fixation composite device 710.The method illustrated in FIG. 7 may also be used for implantation ofcomposite device 10 and other devices according to alternativeembodiments. Composite device 710 comprises a support structure 711 anda thermo-chemically activated thermoplastic matrix 716. The supportstructure 711 comprises a stent-like cage 712 (not shown) and aplurality of rods 714 (not shown).

A percutaneous portal 60 is created into the intramedullary canal 2,preferably in the proximal or distal metaphysial region of the bone. Theopening may not be parallel to the longitudinal axis of the bone; it maybe transverse or at an acute angle relative to the longitudinal axis ofthe bone. If necessary to open the canal space and prepare it for theimplant, the canal is evacuated using a sequence of pulse lavage,brushing, and suction. A delivery tube 62 may be advanced into thepercutaneous portal 60. The composite device 710, in a lengthened andcontracted state, is heated immediately prior to implantation to a firstthermo-chemical state, so that the thermoplastic matrix 716 is above itsglass transition temperature and is therefore plastic and rubbery enoughto be flexed as it is introduced through the percutaneous portal andinto the intramedullary canal. Heating of the composite device 710 toreach the first thermo-chemical state may be accomplished by meansincluding soaking the implant in a hot saline bath, application ofultrasonic vibratory energy, application of radiant heat energy, use ofa local radiation emitter (including ultraviolet, visible light, and/ormicrowave energy), use of a laser energy emitter, use of inductive heatenergy, electrical resistive heating of the cage or the deliveryinstrument, or heating of an expansion apparatus, among others.

The composite device 710 is inserted into the delivery tube 62, pushedthrough the tube and advanced into the intramedullary canal 2 until thecomposite device 710 is contained within the confines of the canal.Optionally, the composite device 710 may be inserted directly throughthe percutaneous portal 60 without passing through a delivery tube 62. Aportion of the composite device 710 may be surrounded by a protectivesheath 749, which is positioned so that it covers the device 710 at thepoint of the bone fracture. The device 710 is then expanded radially. Asthe support structure 711 expands, the stiffening rods 714, the cage 712and thermoplastic matrix 716 move radially outward and are eventuallyaligned along the wall of the intramedullary canal, parallel to thelongitudinal axis of the bone. The composite device 710 is allowed tocool to below the low glass transition temperature T_(g), thus attainingthe second thermo-chemical state, and the matrix 716 crystallizes. Asthe matrix crystallizes it conforms to the shape of the surroundingintramedullary canal, and the cage 712 and stiffening rods 714 are fixedin the thermoplastic matrix 716 along the wall of the canal. The shapeof the intramedullary canal can vary along the length of the bone, withthe canal being generally circular in the diaphysial region near themidpoint of the bone and irregular in the metaphysial regions near theends of the bone. Although the thermoplastic matrix 716 is in agenerally tubular shape as the composite device 710 is inserted, thethermoplastic qualities of the matrix allow it to conform to the shapeof the intramedullary canal around it, and it crystallizes in thatshape, thus providing torsional strength and support to the surroundingbone. The ability of the thermoplastic matrix 716 to conform to theirregularities in the intramedullary canal allows the device 710, andthe stabilized bone, to withstand greater torsional forces than would adevice with a constant circular shape which did not conform to thecanal.

Deformation and/or radial expansion and of the composite device 710 toconform to the intramedullary canal can be accomplished in several ways.A deformation apparatus (such as those shown in FIGS. 16 and 17) may beintroduced into the central core of the composite device 710 before orafter it has been inserted into the intramedullary canal. Thedeformation apparatus is expanded, and forces expansion of the compositedevice 710 until it fills the confines of the canal. The deformationapparatus may comprise a heat source to raise the temperature of thethermoplastic matrix 716. Alternatively, the cage 712 may be constructedwith an outward spring bias, introduced into the intramedullary canaland allowed to expand. In another embodiment which is described indetail below, a balloon apparatus (such as that shown in FIG. 17) isintroduced into the central core of the composite device 710. As theballoon is inflated with heated gas or liquid, it expands, andconsequently induces expansion of the composite device 710. Once thedevice is expanded, the balloon can be deflated and removed. It isappreciated that these deformation and expansion techniques andapparatuses may also be employed with composite device 10 and otherembodiments of intramedullary bone fixation devices disclosed herein.

Referring to FIG. 8, a longitudinal cross-section shows two compositedevices 710, 750 implanted in a bone. Deploying two bone fixationdevices nested in this manner may provide additional strength, rigidityand resistance to torsion than would be available from one bone fixationdevice. Twice the thermoplastic matrix material and twice the supportstructure are present to provide additional stabilization.

Composite device 750 comprises a thermoplastic matrix 756, whichsurrounds a support structure which includes a cage 752 and a pluralityof rods 754. The configuration of matrix 756, cage 752 and rods 754 maybe identical to that of composite device 710. Prior to implantation, thecomposite device 750 is partially radially expanded. The compositedevice 710 is contracted, and slid into a hollow central core 758 of thecomposite device 750. Together, the two devices 710, 750 are heateduntil the thermoplastic matrices 716, 756 reach the firstthermo-chemical state. The two devices 710, 750 are introduced as a unitinto the intramedullary canal. The inner disposed composite device 710is expanded using one of the techniques previously described. As theinner composite device 710 expands, it pushes radially against the outerdisposed composite device 750, forcing it to expand radially until itcontacts and conforms to the wall of the surrounding intramedullarycanal.

Alternatively, composite devices 710, 750 may be introduced individuallyinto the intramedullary canal. Composite device 750 may be introducedfirst, heated and expanded. Composite device 710 is then introduced intothe hollow central core 758 of composite device 750 after is it in theintramedullary canal. After both devices 710, 750 are in the canal,composite device 710 is heated and expanded, pushing radially againstthe outer composite device 750.

The thermoplastic matrix 716 surrounding the composite device 710 maycontact and conform to the thermoplastic matrix 758 of the compositedevice 750. The two devices 710, 750 are allowed to cool to the secondthermo-chemical state and harden.

Referring to FIGS. 9A-9C, three cross-sectional views along differentparts of the bone depicted in FIG. 8 are shown, with devices 710, 750implanted in the intramedullary canal. In FIG. 9A, the intramedullarycanal 2 is relatively wide and circular in shape, resulting in a widecircular central hollow core 718. Also, the thermoplastic matrices 716,756 are relatively thin, and the rods 714, 754 are spaced relatively farapart, as the devices 710, 750 had to expand radially farther to contactthe wall of the intramedullary canal at that point. As seen in FIG. 9B,at this point along the bone the intramedullary canal is smaller indiameter and more irregular in shape. The thermoplasticity of thematrices 716, 756 allows the devices 710, 750 to match the size andshape of the canal. As seen in FIG. 9C, at this point along the bone theintramedullary canal is narrow in cross-section and substantiallytriangular in shape. According, the thermoplastic matrices 716, 756 arethicker and the rods 714, 754 are closer together, since the devices710, 750 are relatively less expanded.

Referring to FIG. 10, an alternative embodiment of an intramedullarybone fixation composite device is shown in a cutaway view. Compositedevice 810 comprises support structure 811 and a thermo-chemicallyactivated thermoplastic matrix 816. Support structure 811 comprises acage 812, a plurality of rods 814, and a plurality of sutures 815 whichconnect the cage to the rods. The thermo-chemically activated matrix 816surrounds the cage 812, rods 814 and sutures 815 such that they areembedded in the matrix. The sutures 815 are interwoven around andbetween the cage 812 and the rods 814 to connect the cage 812 to therods 814 in a manner that allows regulated movement of the cage 812 andthe rods 814 relative to one another.

Alternately, the sutures may be knit into a sleeve that holds the arrayof rods and surrounds the cage. The interweaving may be constructed insuch a way as to allow radial expansion of the cage 812 and the rods 814from a contracted position in which the cage 812 is lengthened and therods 814 are tightly packed together, to an expanded position in whichthe cage 812 is shortened, radially expanded and the rods 814 arearrayed around the cage with relatively more space between each rod. Thecage 812 may comprise web-like stent material similar to stents depictedin FIGS. 3A-31, or may comprise another woven or laser cut stent-likematerial. The rods 814 may be similar to the rods 14 depicted in FIG. 5.The thermo-chemically activated thermoplastic matrix 816 may be similarto the thermo-chemically activated thermoplastic matrix 16 describedpreviously and depicted in FIG. 6. The sutures may comprise any ofseveral commercially available sutures, including Dyneema Purity® UltraHigh Molecular Weight Polyethylene (UHMWPE), or bioabsorbablemultifilament polylactic acid (PLA) sutures such as PANACRL™, amongothers.

Composite device 810 may be introduced into the intramedullary canal inthe same manner as previously described for composite device 710. Energyis applied to composite device 810, heating it until thethermo-chemically activated matrix 816 reaches the first thermo-chemicalstate and is flexible and rubbery. The composite device 810 iscontracted so that it is sufficiently flexible to be inserted into theintramedullary canal through an opening in the bone, an opening whichmay not be parallel to the intramedullary canal. The composite device810 is inserted into the canal and expanded by one of the expansionmethods previously described. When the device is expanded within theintramedullary canal, the thermo-chemically activated matrix 816contacts and is conformed to the walls of the intramedullary canal. Thedevice 810 is allowed to cool and the thermo-chemically activated matrix816 attains the second thermo-chemical state, and hardens sufficientlyto fix the support structure 811 in its expanded position within theintramedullary canal.

Referring to FIGS. 11A-11E, a series of five cross-sectional viewsillustrate the expansion of composite device 810 from a contractedposition to a fully expanded position. Beginning with FIG. 11A, a hollowcentral core 818 of composite device 810 is substantially circular. Ascomposite device 810 expands, the cage 812 and the hollow central core818 increase in diameter and the thermoplastic matrix 816 stretches tofit around the cage 812. At the most expanded state illustrated in FIG.11E, the thermoplastic matrix 816 is substantially thinner than at themost contracted state. In FIG. 11A, the array of rods 814 are relativelyclosely packed near one another; in FIG. 11E they are spread apart andare substantially equidistantly arrayed about the hollow central core818.

FIGS. 12A-12E illustrate an alternative embodiment of a composite devicein five cross-sectional views. Similar to composite device 810,composite device 910 comprises a support structure 911 with a cage 912,a plurality of rods 914, and a plurality of sutures 915 which connectthe cage to the rods. A thermo-chemically activated thermoplastic matrix916 surrounds the cage 912, rods 914 and sutures 915 such that they areembedded in the matrix. As most clearly seen in FIG. 12C, in thisembodiment, the thermoplastic matrix 916 is configured in a series offolds 917, as compared to the circular configuration seen forthermoplastic matrix 816 in FIG. 11C. The folded configuration of thethermoplastic matrix 916 results in a star-shaped hollow central core918. The star-shaped hollow central core 918 is smaller in terms ofcross-sectional open space, as much of the space is taken up by thefolds of the thermoplastic matrix 916. Therefore, the thermoplasticmatrix 916 is thicker in this embodiment than in other embodiments suchas device 810. Thus, as seen in FIG. 12E, the fully expanded compositedevice 910 has a thicker thermoplastic matrix, which may result inadditional support for the surrounding bone during the healing process.

Composite device 910 may be introduced into the intramedullary canal inthe same manner as previously described for composite devices 710 and810. Energy is applied to composite device 910, heating it until thethermo-chemically activated matrix 916 reaches the first thermo-chemicalstate, and is flexible and rubbery. The composite device 910 iscontracted into the deeply folded position seen in FIG. 12A, so that itis sufficiently flexible to be inserted into the intramedullary canalthrough an opening in the bone. The composite device 910 is insertedinto the canal and expanded by one of the expansion methods previouslydescribed. A specifically configured implant expander such as astar-shaped balloon expansion device (not shown) may be used to expandthe device 910. When the device is expanded within the intramedullarycanal, the thermo-chemically activated matrix 916 contacts and isconformed to the walls of the intramedullary canal. The device 910 isallowed to cool and the thermo-chemically activated matrix 916 attainsthe second thermo-chemical state, and hardens sufficiently to fix thecage 912 and rods 914 in their expanded positions within theintramedullary canal. In the case of a larger bone, two compositedevices 910 may be deployed, one inside the other, to provide additionalsupport to the bone.

Referring to FIGS. 13A and 13B, one alternative embodiment of a supportstructure 71 suitable for use in an intramedullary bone fixation devicehas an hourglass shape. In the context of the present invention, anhourglass shape is a generally longitudinal, columnar shape in which thetwo end portions of the column are wider in diameter than a middleportion of the column. The support structure 71 comprises a cage 72 androds 14. In this embodiment, the diameters of cage ends 74, 76 aregreater than the diameter of a cage sleeve 78. In order to clearly viewthe configuration of cage and rods, a thermoplastic matrix is not shown.A matrix similar to that of the thermoplastic matrix 16 of FIG. I may beused in conjunction with support structure 71, or it may have adifferent configuration. The hourglass shape enables the tubular supportstructure 71 to conform to the contours of the intramedullary canal of along bone, in which the metaphysial regions at the ends of the bone areirregular and may be greater in diameter than the diaphysial region nearthe midpoint of the bone. In the embodiment depicted, the hourglassshape is achieved by the particular threading of the rods within thestent portion of the cage. At the first 74 and second 76 ends, the rods14 are contained within the confines of the cage 72; toward the centerof the sleeve 78, the cage is contained within the circle of the rods14. In FIG. 13A, the support structure 71 is shown in the contractedstate (for insertion or removal); in FIG. 13B, the expanded state isshown. The support structure 71 may be inserted in the same manner asdescribed previous for support structure 11, and the same expansionmethods described previously may be used to expand the support structure71.

One alternative embodiment of an intramedullary bone fixation device(not shown) comprises a laser-cut cage which is constructed with anoutward spring bias. In this embodiment, the device is compressed priorto implantation by holding the rods steady and pulling longitudinally onthe cage. The web-like configuration of the cage permits the cage tolengthen while simultaneously its core diameter contracts, enabling thedevice to be narrow and flexible enough for insertion. The device isintroduced into the intramedullary canal and the cage is released. Uponrelease, the outward spring bias of the cage causes the cage to expandradially and simultaneously shorten. Radial expansion continues untilthe outer perimeter of the device contacts the inner wall of theintramedullary canal. The web-like configuration of the cage also allowsit to conform to variations in the geometry of the intramedullary canal.This embodiment may also include the thermoplastic matrix, wherein priorto the compression step described above, the thermoplastic matrix isheated to the first thermo-chemical state, so it is flexible as thedevice is compressed, inserted and expanded. After insertion and radialexpansion, the energy is allowed to dissipate and the thermoplasticmatrix attains the hardened second thermo-chemical state.

Referring to FIGS. 14A through 14D, another alternative embodiment ofthe invention comprises a cage with an outward spring bias, which may beused in conjunction with a thermoplastic matrix such as that depicted inFIGS. 1 and 6. FIG. 14A is a perspective view of a cage 112, cut with aplurality of accordion-type folds 114 which unfold as the cage expandsradially. Alternating with the folds 114 are longitudinal ribs 116, anda hollow central core 115 extends the length of the cage 112. Each rib116 has a longitudinal channel I 18 which may hold a stiffening rod. Thecage may be laser-cut or machined from metal, or may comprise a plasticmaterial or a thermo-chemically activated thermoplastic matrix material,as described above. The cage 112 may have a straight shape with aconstant diameter, or may have an hourglass shape in which the two endsare wider than the central section. Other shapes may alternatively beused for different bone morphologies.

FIG. 14B is an end view of the cage 112 in a compressed state, showingthe tight compaction of the folds 1 4 and ribs 116. FIG. 14C is aperspective view of the cage 112 after radial expansion, and FIG. 14D isan end view of the expanded cage 112. In this embodiment, the supportstructure can be compressed for implantation by a binding material whichis wrapped or tied around the compressed cage. After insertion into theintramedullary canal, the cage is released by cutting or removal of thebinding material. Once released, the outward spring bias of the cage 112causes the cage 112 to expand radially in the same manner as describedfor the previous embodiment.

In another embodiment the support structure may be monolithic; that is,formed as a single unit. The cage and rods are formed together, such asby a machining process and remain connected together. Referring to FIG.15, an embodiment of a monolithic support structure 111 is shown in anexpanded state. This embodiment has no channels for rods, butconsequently has ribs 117 between the accordion folds 114 which aresolid and comprise more material, thus providing rigidity similar to therods of other embodiments. Between the ribs 117, the accordion folds 114have a plurality of slots 119. The slots 119 allow for less material andthus more flexibility of the support structure when compressed.Additionally, when compressed, the tight packing of the ribs 117 betweenthe accordion folds 114 allows the support structure 111 to flexsufficiently for insertion into the intramedullary canal. The monolithicsupport structure 111 may be used in conjunction with a thermoplasticmatrix. Contraction, insertion and expansion of the monolithic supportstructure 111 may be in the same manner as described previously for thecage 112.

In another embodiment of the invention, at least two support structuresand/or cages such as those depicted in FIGS. 14 and 15 can be nested,one within the other. A first support structure 111 or cage 112 embeddedin the thermoplastic matrix 16 is heated to the first thermo-chemicalstate, compressed, inserted into the intramedullary canal, and expanded.A second support structure 111 or cage 112 embedded in the thermoplasticmatrix 16 is similarly compressed and inserted into the central core 115of the first support structure. When the second structure 111 or cage112 expands, it pushes radially against the first structure 111 or cage112. As described previously for other embodiments, the thermoplasticmatrix 16 surrounding the first support structure conforms to thecontours of the intramedullary canal. Within the first supportstructure, the thermoplastic matrix 16 surrounding the second supportstructure conforms to the surrounding first support structure. Thematrix material surrounding both the first and second structures coolsto the second thermo-chemical state and crystallizes. This double layerof matrix material and support structures provides enhanced support andrigidity to the surrounding bone.

The cage 112 and support structure 111 embodiments depicted in FIGS. 14and 15 can alternatively be constructed without an outward spring bias.The compressed cage 112 or support structure 111 may be surrounded bythe thermoplastic matrix 16. As described previously, the device isheated so the thermo-plastic matrix 16 reaches the first thermo-chemicalstate and the device is flexed and inserted into the intramedullarycanal. In this case, an expansion apparatus or balloon mechanism aspreviously described, or other expansion mechanism is inserted into thecentral core 115 and used to expand the device after it is implanted.Once the device is expanded, energy dissipates into the surroundingtissue, the matrix attains the second thermo-chemical state, and thecage 112 or support structure 1 is fixed within the cooled, crystallizedmatrix 16. The expansion apparatus, balloon mechanism, or otherexpansion mechanism may then be removed from the central core 115.

One alternative embodiment of an intramedullary bone fixation compositedevice (not shown) comprises a thermoplastic matrix which is notcontinuous along the entire length of the corresponding cage or supportstructure. In this embodiment, the matrix comprises at least twoseparate tube-like portions, each of which surrounds one end of the cageor support structure and extends partway along the sleeve. Thisdiscontinuous configuration of the matrix contributes to an hourglassshape and allows less matrix material to be used. This matrixconfiguration can be used with either a cage with an outward springbias, or with a cage with no outward spring bias.

Another alternative embodiment of an intramedullary bone fixationcomposite device (not shown) comprises a support structure whichcomprises at least one rod, and no cage. Prior to implantation, thematrix is heated to the first thermo-chemical state and formed into atubular shape around the rods, which are subsequently embedded in thematrix. The device is flexed and inserted into the patient. While thematrix is still in the first thermo-chemical state, an expansionapparatus or balloon is inserted into the center of the tubular deviceand used to expand the device within the intramedullary canal. As thedevice expands, the rods and the matrix material are pushed radially tothe inner wall of the intramedullary canal. After expansion, the deviceis allowed to cool to the second thermo-chemical state, and the matrixhardens, fixing the rods in their positions around the inner wall of thecanal.

Another alternative embodiment of an intramedullary bone fixation device(not shown) comprises a support structure which comprises a cagemanufactured of the thermoplastic matrix material, and rods. Duringmanufacture the matrix material is heated above its T_(g) and extrudedinto a cage-like form. During or after extrusion the rods areinterwoven, braided in, or otherwise attached as described previously.To implant the device, the device is heated above the T_(g) of thematrix to attain the first thermo-chemical state, contracted, flexed,inserted and expanded as described previously.

FIGS. 16A and 16B illustrate an implant expansion device which may beused to deform and expand several of the intramedullary bone fixationdevices described previously, such as composite device 10, compositedevices 710, 750 and 810, a device incorporating support structure 71,or other devices which incorporate a cage or support structure withoutan outward spring bias. A mechanical expansion apparatus 500 islongitudinally insertable into the central core of the intramedullarybone fixation device. As seen in FIG. 16A, the mechanical expansionapparatus 500 has a shaft 514, which extends from a first end 510 to asecond end 512. An adjustment nut 516 is threaded onto a threadedportion 515 of the shaft 514, adjacent the first end 510. A cone-shapedfirst expander guide 518 is also threaded onto the threaded portion 515of the shaft 514, on the opposite side of the adjustment nut 516 fromthe first end 510. The second end 512 of the shaft 514 terminates in acone-shaped second expander guide 519. The shaft 514 comprises ametallic material, and is sufficiently thin and flexible to be insertedinto the central core of an intramedullary bone fixation while thedevice is in the intramedullary canal of a bone in a patient.

Referring to FIG. 16B, strung on the central shaft 514 and listed intheir order of occurrence from the first expander guide 518 to thesecond expander guide 519 are: a first expander segment 520, a pluralityof core segments 522, a central segment 524, another plurality of coresegments 522, and a second expander segment 526. The core segments 522and the central segment 524 comprise a relatively rigid material, whilethe expander segments 520, 526 comprise a relatively rubbery, flexiblematerial. The first expander segment 520 surrounds a portion of thefirst expander guide 518 in a sleeve-like manner, and the secondexpander segment 526 similarly surrounds a portion of the secondexpander guide 519 in a sleeve-like manner. The core segments 522,central segment 524, and expander segments 520, 526 are initially placedloosely on the shaft 514 with space between each segment, so that theapparatus can flex while being inserted into the central core of theintramedullary bone fixation device.

After the intramedullary bone fixation device with a thermoplasticmatrix (not shown) is placed in the intramedullary canal, the mechanicalexpansion apparatus 500 may be inserted through the delivery tube 62(not shown) into the central core of the intramedullary bone fixationdevice. Then the adjustment nut 516 is turned, forcing the firstexpander guide 518 to advance along the shaft 514 toward the secondexpander guide 519 at the second end 512. The first expander segment520, core segments 522, central segment 524, and second expander segment526 are compressed together as they are held between the first andsecond expander guides 518, 519. The rubbery, flexible expander segments520, 526 expand radially as they are forced farther onto the cone-shapedexpander guides 518, 519. As the expander segments 520, 526 expandradially, they push the ends of the surrounding intramedullary bonefixation device outward radially, thus matching the generally hourglassshape of the intramedullary canal. Expansion is ceased when the outerperimeter of the intramedullary bone fixation device contacts the innerwalls of the intramedullary canal. The expansion apparatus 500 may bekept in the central core of the intramedullary bone fixation deviceuntil the thermoplastic matrix cools to the second thermo-chemicalstate. The expansion apparatus 500 is contracted by turning theadjustment nut 516 in the opposite direction, and the apparatus 500 isthen removed from the central core.

The expansion apparatus 500 may optionally include a heating element. Inthis configuration, it can heat the thermoplastic matrix of anintramedullary bone fixation device while in a patient, in order toadjust the conformity of the matrix within the intramedullary canal.

Referring to FIGS. 17-21, an alternative method to deform and expand anintramedullary bone fixation device comprises an implant deformer whichis a balloon expansion apparatus. As seen in FIG. 17, a balloonexpansion apparatus 600 configured to fit within a composite device 10in the intramedullary canal of a bone comprises an elastic bladder 602with an opening 604. A set of flexible hoses comprising an input hose606 and an output hose 608 are configured to extend from a regulatorapparatus 610, through the opening 604 and into the elastic bladder 602.The regulator apparatus 610 is external to the patient, and comprises apump to regulate flow, and a temperature regulator to regulate thetemperature, of liquid which can flow into and out of the elasticbladder 602. FIG. 17 depicts the hoses adjacent and parallel to oneanother; however they may be configured in alternative arrangements,including a concentric arrangement in which one hose surrounds theother. The hoses 606, 608 terminate at differing positions within thebladder 602.

Referring to FIG. 18, a composite device 710 with a balloon expansionapparatus 600 already inserted into the central core 718 is introducedinto the intramedullary canal of a bone. Introduction into the bone canbe through the method described previously, in which the compositedevice (with the balloon apparatus in the central core) is heated sothat the matrix attains the first thermo-chemical state. The compositedevice 710 plus balloon apparatus 600 are flexed and introduced into theintramedullary canal through the percutaneous portal 60. A delivery tube62 (not shown) may optionally be used during the introduction andexpansion procedures. The input 606 and output 608 hoses are insertedthrough the balloon opening 604 ideally before the composite device 710plus balloon apparatus 600 are introduced into the intramedullary canal,but can optionally be inserted into the balloon opening 604 afterintroduction into the intramedullary canal. A protective sheath 49 maysurround the composite device 710 at the location of the bone fracture.

Referring to FIG. 19, after the composite device 10 plus balloonapparatus 600 are within the intramedullary canal, inflation of thebladder 602 may begin. The external regulator apparatus 610 (not shown)pumps heated liquid such as water or saline solution, among others,through the input hose 606 into the elastic bladder 602. The heat of theliquid maintains the thermoplastic matrix 716 of the composite device710 at the deformable first thermo-chemical state. As the heated liquidfills the bladder 602, the bladder expands. Contained within thecomposite device 710, the bladder 602 eventually pushes outward,inducing radial expansion of the composite device 710. As describedpreviously, cage and rod components of the support structure 711 areconnected in a web-like construction which allows them to expandradially. The thermoplastic matrix 716 surrounding the support structure711 is at the heated first thermo-chemical state and is pushed radiallyby the expanding support structure, conforming to the surroundingintramedullary canal walls. The flexible, rubbery character of thematrix allows it to fit into the natural morphological variations in thewall of the intramedullary canal. A mesh-like end cap 746 on a secondend 732 of the composite device 710 prevents the elastic bladder 602from escaping or ballooning out of the second end 732. The output hose608, which terminates at a location different from that of the inputhose 606, allows liquid to flow out of the balloon apparatus 600. Theregulator apparatus 610 maintains the flow, temperature and pressure ofthe liquid.

FIGS. 20A-20C display cross-sections of the bone and the compositedevice 710 at three different locations along the length of the boneshown in FIG. 19. At cross-section A-A in FIG. 20A, the cross-sectionalshape of the intramedullary canal is relatively circular. The device 710has expanded to the wall of the canal, the matrix 716 is relativelythin, and the rods 714 are spaced relatively far apart. At cross-sectionB-B in FIG. 20B, the canal is smaller and more rectangular in shape thanat cross-section A-A. However, the deformable nature of the matrix 716allows the matrix and the entire composite device 710 to expanddifferentially and conform to this variation in shape of theintramedullary canal. At cross-section C-C in FIG. 20C, thecross-sectional shape of the intramedullary canal is relatively smaller,and has a triangle-like shape. Again, the matrix 716 and the compositedevice 710 can conform to this irregular shape. The rods 714 arerelatively closer together and the matrix 716 is relatively thicker. Theability of the composite device 710 to closely conform to the confinesof the intramedullary canal allows the device to withstand greatertorsional forces than would a device with a constant circular shapewhich did not conform to the canal.

Referring to FIG. 21, the balloon expansion apparatus 600 is depictedbeing withdrawn from the composite device 710. After expansion of theelastic bladder 602 is accomplished as described previously, the liquidin the elastic bladder 602 may be cooled by pumping cool liquid inthrough input hose 606 and withdrawing warmer liquid through output hose608 until a consistently cooler liquid is in the bladder 602. The coolerliquid in the bladder absorbs thermal energy from the matrix 716,allowing it to cool and transform from the flexible firstthermo-chemical state to the hardened second thermo-chemical state. Oncethe composite device 710 has thus cooled and hardened, the remainingliquid may be pumped out of the elastic bladder 602, and the balloonexpansion device 600 is pulled out of composite device 710 through thepercutaneous portal 60.

A protective, tubular insertion sheath (not pictured) may surround allor a portion of any of the above-described intramedullary bone fixationdevices during the implantation procedure, and may optionally be removedfollowing implantation. The insertion sheath may be very thin, and mayprevent portions of the support structure or matrix from snagging on orscratching the intramedullary canal, or portions of the fractured bone.Once the device is inserted, the sheath may be removed by being pullingthe sheath out through the delivery tube, while leaving the devicebehind.

With any embodiment of the device, after insertion of the device butbefore conclusion of the implantation procedure, x-ray, fluoroscopy, orother radiographic methods may be implemented to assess the alignment ofthe device relative to the bone. If alignment is unsatisfactory, aheating element (not shown) or a heatable expansion device such as theballoon apparatus 600 or mechanical expansion apparatus 500 as describedpreviously may be introduced into the central core. The device is heatedso the thermoplastic matrix again reaches first thermo-chemical state,and the device may then be removed and reinserted or otherwise adjusteduntil a satisfactory alignment is achieved. The device is allowed tocool, so the thermoplastic matrix returns to the second thermo-chemicalstate through the natural dissipation of energy into the surroundingtissue.

Post-implantation, the device may be removed if desired. The method ofremoval will vary, depending on the state of the decomposition of thebiocompatible thermoplastic matrix. If the thermoplastic matrix is stillintact, a percutaneous portal may be opened and a tube may be inserted.The tube may be the same as or similar to the delivery tube 62 describedpreviously. A heating element or heatable expansion apparatus such asthe mechanical expansion apparatus 500 or balloon expansion apparatus600 is introduced into the central core, and the device is heated untilthe matrix reaches the first thermo-chemical state, above the glasstransition temperature. The heat source is removed; the device may becontracted by holding the rods steady and pulling longitudinally on thecage. The device may be removed through the delivery tube, or directlythrough the percutaneous portal. If the thermoplastic matrix has beensufficiently absorbed so that it is no longer intact, no heating isrequired; the device is contracted and removed.

Another embodiment of the invention (not shown) comprises a supportstructure and an alternative form of the thermoplastic matrix,comprising an injectable form of a synthetic biodegradable polymer,poly-D,L-lactic acid-polyethyleneglycol (PLA-PEG). This biodegradablecomposite is temperature-sensitive so that when it is heated it takes ona liquid, semi-solid form and following injection, cools and becomessemi-solid. A structure such as support structure 11, 711, 811 or 71 isintroduced into the intramedullary canal. The structure may have aprotective sheath surrounding the portion of the structure which will beadjacent to the fracture location. Following insertion of the supportstructure into the intramedullary canal, and radial expansion of thesupport structure, heated PLA-PEG is injected through a flexible tube orcatheter which is inserted through the delivery tube 62 into the centralcore. The liquid PLA-PEG flows through the web-like support structure,filling the canal and surrounding the support structure. The protectivesheath prevents the PLA-PEG from contacting the fractured area of thebone. The PLA-PEG is allowed to cool and harden, and provides rigidsupport around the structure.

Referring to FIG. 22A, a perspective view shows another embodiment ofthe invention, comprising a telescoping intramedullary fixation device210. This device comprises a central wire 212 surrounded by a series offive tubular nesting components 213-217. Each tubular nesting componentis substantially the length of the entire device 210 when all componentsare nested together, and each successive nesting component is slightlywider in diameter than the component it surrounds. Other embodiments ofthe telescoping intramedullary fixation device 210 may have fewer, ormore, than five nesting components. The central wire 212 may have asolid core and may not be tubular, but is slender and thus sufficientlyflexible to be inserted into the intramedullary canal. The nestingcomponents 213-217 may comprise metal, a biocompatible polymer material,or a mesh-like stent material (such as those depicted in FIG. 3), andmay be embedded in a thermoplastic matrix material. FIG. 22A displaysthe telescoping device 210 in a fully extended or telescoped position;however when completely implanted in a patient the device 210 is in acollapsed position in which the nesting components are concentricallynested together.

The first nesting component 213 surrounding the central wire 212 isslightly wider in diameter than the central wire 212. Each successivenesting component 214-217 is slightly wider than the preceding one, andas the nesting components increase in diameter, the width of the wall ofthe component may decrease so that each nesting component is stillflexible enough to be inserted into the canal. The wall thickness ofeach of the nesting components 213-217 may advantageously be selectedsuch that the nesting components 213-217 are all nearly equallyflexible. According to one alternative embodiment (not shown), thenesting components do not have solid walls but have slots in the wallsto increase flexibility.

In a patient, the central wire 212 may first be inserted into theintramedullary canal. Then, successive nesting components 213-217 withincreasing diameters are introduced into the intramedullary canal. Thenesting component 213 with the smallest diameter is slid in around thecentral wire 212; the nesting component 214 with the next largestdiameter is slid in surrounding the first nesting component 213, and theremaining nesting components 215-217 are inserted in a similar fashion.The largest nesting component 217 fits just inside the walls of thecanal. After the components are inserted and collapsed together, aninjectable, hardenable polymer such as bone cement or a biocompatiblepolymer such as PLA-PEG may be introduced into the canal to fill anyspaces between the largest nesting component 217 and the wall of thecanal. The largest nesting component 217 may have a sheath 219 whichprevents the polymer from accessing the fractured area of the bone, asdescribed previously. The nested set of nesting components 213-217 has acombined strength and rigidity which exceeds that of any of theindividual nesting components, and the device 210 provides strength andsupport during bone healing.

FIG. 22B is an enlarged, stylized cross-sectional view of the connectionbetween nesting components 216 and 217; however the figure isrepresentative of the connections between each of the nesting components213-217. Nesting component 217 has a first end 230 with aninward-projecting first lip 234. The next smallest nesting component 216has a second end 232 with an outward-projecting second lip 236. Theprojecting lips 234, 236 allow for easy removal of the apparatus. Duringremoval, initially a slap hammer is used to break the largest nestingcomponent 217 away from the bone cement. Nesting component 217 is pulledout first, and its inwardly-projecting lip 234 hooks theoutwardly-projecting lip 236 of the next largest nesting component 216,and causes it to be pulled out next, followed by the next largestnesting component 215, until all the nesting components 213-217 arepulled out. The central wire 212 is removed separately after all thenesting components are removed.

Referring to FIG. 23, another embodiment of a telescoping fixationdevice is shown in an extended state. In this embodiment, telescopingfixation device 310 comprises a series of nesting components 313-317,each of which comprises a mesh-like stent portion embedded inthermoplastic matrix material 318 similar to that of the thermoplasticmatrix 16 of FIGS. 1 and 6. Each nesting component 313-317 issubstantially the length of the entire device 310 when all componentsare nested together. Prior to implantation, the device 310 is heated asdescribed previously so that the thermoplastic matrix material 318reaches the first thermo-chemical state, and is rubbery and flexible.The device 310 is telescoped out into an extended configuration, andintroduced into the intramedullary canal through an opening transverseto the longitudinal axis of the bone. The central wire 312 is introducedfirst, and the adjacent and smallest nested component 313 is inserted soit nests around the central wire. The next smallest nested component 314is nested about the smallest nested component 313, and so on until allthe remaining nested components 315-317 are introduced into theintramedullary canal and nested together. The device 310 is allowed tocool so that energy dissipates into the surrounding tissue, and thethermoplastic matrix material 318 of each nesting component 313-317reaches the second thermo-chemical state, and hardens.

Referring to FIG. 24, another alternate embodiment of a telescopingfixation device is shown in a partially extended state. In thisembodiment, telescoping fixation device 410 comprises a series ofnesting components 413-417, which are helically threaded so that duringimplantation each nesting component is threaded onto the precedingsmaller component. The direction of the threading on each nestingcomponent may alternate, so that each nesting component is threaded ontothe next nesting component in the opposite direction from the previousone. Each nesting component 413-417 is substantially the length of theentire device 410 when all components are nested together. As withdevices 210 and 310, five nesting components are described, however inalternate embodiments the number and size of the nesting components mayvary.

Similar to the telescoping fixation devices 210 and 310, device 410 hasa central wire 412 which is initially inserted into the intramedullarycanal through a delivery tube 62 or similar interface. The first nestingcomponent 413 is slid in around the central wire. The first nestingcomponent 413 is tubular in form has a clockwise helical protrusion 420which protrudes on the outside of the tube, winding in a clockwisedirection along the length of the nesting component 413.

Referring to FIGS. 25A-25B, two adjacent helically threaded nestingcomponents have threading configurations which wind in oppositedirections. As seen in FIG. 25A, the second nesting component 414 has aclockwise helical slot 422 which winds clockwise along its length, and acounter-clockwise helical protrusion 421 which winds counter-clockwisealong its length. As nesting component 414 is inserted into theintramedullary canal, it is twisted clockwise so that its clockwisehelical slot 422 fits over the clockwise helical protrusion 420 on thefirst nesting component 413. As seen in FIG. 25B, the third nestingcomponent 415 has a counter-clockwise helical slot 423, and a clockwisehelical protrusion 420. It is inserted and threaded onto the secondnesting component 414 in a counter-clockwise fashion, so that itscounter-clockwise helical slot 423 engages with the counter-clockwisehelical protrusion 421 on the second nesting component 414. Eachremaining nesting component is threaded clockwise or counter-clockwiseto engage with the smaller component nested inside of it. The outermostnesting component 417 may or may not have a helical protrusion.

The helical threading system varies in direction so that the entiredevice will not be loosened when the outermost component 417 is turnedin one direction. In addition, this bi-directional threading system addsoverall torsional strength to the telescoping fixation device 410, sincea twisting force in one direction will not disengage all the threadingon the nesting components.

The telescoping fixation device 410 may be used in conjunction with aninjectable hardenable polymer, such as bone cement or a biocompatiblepolymer such as PLA-PEG, among others. The fixation device 410 may beimplanted as described previously, and the injectable polymer may thenbe injected into the intramedullary canal around the periphery of thedevice, to fix the device in place. The outermost nesting component 417may have a protective sheath 419 which prevents the polymer fromaccessing the fractured area of the bone, as described previously.Removal of the device 410 is accomplished by breaking the device awayfrom the polymer as described previously, then unthreading and removingeach component 413-417 in a clockwise or counter-clockwise direction,beginning with the outermost component 417 and proceeding inward.

The present invention may be embodied in other specific forms withoutdeparting from its spirit or essential characteristics. It isappreciated that various features of the above-described examples can bemixed and matched to form a variety of other alternatives. For example,support structure and matrix materials and configuration features canvary, as can the method used to expand the device. As such, thedescribed embodiments are to be considered in all respects only asillustrative and not restrictive. The scope of the invention is,therefore, indicated by the appended claims rather than by the foregoingdescription. All changes which come within the meaning and range ofequivalency of the claims are to be embraced within their scope.

1. A thermo-chemically activated composite device for bonestabilization, the composite device comprising: a thermo-chemicallyactivated thermoplastic matrix which is sufficiently deformable toconform to a bone at a first thermo-chemical state and sufficientlyhardened to stabilize the bone at a second thermo-chemical state; and asupport structure connected to the thermo-chemically activatedthermoplastic matrix to support the thermo-chemically thermoplasticmatrix.
 2. The composite device of claim 1, wherein the supportstructure passes through the thermo-chemically activated thermoplasticmatrix.
 3. The composite device of claim 1, wherein thethermo-chemically activated thermoplastic matrix is capable of beingrepetitively transformed from the first thermo-chemical state to thesecond thermo-chemical state, and from the second thermo-chemical stateto the first thermo-chemical state.
 4. The composite device of claim 1,where the thermo-chemically activated thermoplastic matrix is capable ofbeing transformed from the second thermo-chemical state to the firstthermo-chemical state by application of energy to the thermo-chemicallyactivated thermoplastic matrix from an outside source and is capable ofbeing transformed from the first thermo-chemical state to the secondthermo-chemical state by dissipation of energy from thethermo-chemically activated thermoplastic matrix to surrounding matter.5. The composite device of claim 1, wherein the composite device iscapable of being implanted in a patient while the thermo-chemicallyactivated thermoplastic matrix is at the first thermo-chemical state,the thermo-chemically activated thermoplastic matrix is transformable tothe second thermo-chemical state while the composite device is in thepatient, and the composite device is configured to remain in the patientuntil the thermo-chemically activated thermoplastic matrix returns tothe first thermo-chemical state.
 6. The composite device of claim 1,wherein the thermo-chemically activated thermoplastic matrix isbiocompatible and comprises a polymer selected from the group consistingof polylactic acid (PLA), poly ε-caprolactone (PCL), trimethylenecarbonate (TMC), polyglycolic acid (PGA), poly l-lactic acid (PLLA),poly d-l-lactide (PDLLA), polyethylene terephthalate (PET), aliphaticpolyesters, polyanhydrides, polyphosphazenes, polyorthoesters,poly(p-dioxane), polyaminoacids, pseudopolyaminoacids, erodablehydrogels, and natural polymers.
 7. The composite device of claim 6,wherein the thermo-chemically activated thermoplastic matrix furthercomprises a blend of polymers selected from the group consisting ofpolylactic acid (PLA), poly ε-caprolactone (PCL), trimethylene carbonate(TMC), polyglycolic acid (PGA), poly l-lactic acid (PLLA), polyd-l-lactide (PDLLA), polyethylene terephthalate (PET), aliphaticpolyesters, polyanhydrides, polyphosphazenes, polyorthoesters,poly(p-dioxane), polyaminoacids, pseudopolyaminoacids, erodablehydrogels, and natural polymers, wherein the blend of polymers has aglass transition temperature selected to be near the body temperature ofa patient.
 8. The composite device of claim 6, wherein thethermo-chemically activated thermoplastic matrix further comprises abioactive material, wherein the bioactive material is selected toenhance healing of the bone, wherein the bioactive material is selectedfrom the group consisting of hydroxyl apatite, tetracalcium phosphate,β-tricalcium phosphate, fluorapatite, magnesium whitlockite,β-whitlockite, apatite/wollastonite glass ceramic, calcium phosphateparticle reinforced polyethylene, bioactive glasses, bioactive glassceramics, polycrystalline glass ceramics, and polyethylene hydroxylapatite.
 9. The composite device of claim 1, wherein the supportstructure comprises an elongated shape having a longitudinal axis,wherein the composite device is capable of radial expansion from acontracted state into an expanded state, wherein the support structureis further capable of greater flexion about the longitudinal axis whilein the contracted state than while in the expanded state.
 10. Thecomposite device of claim 1, wherein the composite device is shaped tobe implanted into an intramedullary canal of the bone.
 11. The compositedevice of claim 10, wherein the composite device is implantable into theintramedullary canal along a pathway that is not parallel to theintramedullary canal.
 12. The composite device of claim 10, wherein thecomposite device is removable from the intramedullary canal of the boneafter healing of the bone.
 13. The composite device of claim 10, whereinthe thermo-chemically activated thermoplastic matrix is configured toconform to the shape of the intramedullary canal.
 14. The compositedevice of claim 1, wherein the support structure comprises at least onerod.
 15. The composite device of claim 14, wherein the support structurecomprises an array of rods interconnected such that the array is capableof radial expansion from a contracted state to an expanded state. 16.The composite device of claim 1, wherein the support structure comprisesa cage.
 17. The composite device of claim 16, wherein the cage iscapable of radial expansion and contraction.
 18. The composite device ofclaim 17, wherein the cage has an hourglass-like shape selected toconform to the intramedullary canal of the bone.
 19. The compositedevice of claim 17, wherein the support structure further comprises atleast one rod, wherein the rod is retained by the cage.
 20. Thecomposite device of claim 19, wherein the cage and the rod are formedsubstantially of metallic materials.
 21. The composite device of claim1, wherein the support structure comprises a plurality of nestedcomponents which are telescopically extendable.
 22. The composite deviceof claim 1, further comprising a first composite device and a secondcomposite device, wherein the first composite device is configured to benestable inside the second composite device within the intramedullarycanal of the bone.
 23. A thermo-chemically activated device for internalbone stabilization, the device comprising: a thermo-chemically activatedthermoplastic matrix which is sufficiently deformable to conform to abone at a first thermo-chemical state and sufficiently hardened tostabilize the bone at a second thermo-chemical state; wherein thethermo-chemically activated thermoplastic matrix comprises an elongatedshape selected to enable insertion of the thermo-chemically activatedthermoplastic matrix into an intramedullary canal of the bone.
 24. Thedevice of claim 23, wherein the thermo-chemically activatedthermoplastic matrix is configured to conform to the shape of theintramedullary canal.
 25. The device of claim 23, wherein the device isimplantable into the intramedullary canal along a pathway that is notparallel to the intramedullary canal.
 26. The device of claim 23,wherein the thermo-chemically activated thermoplastic matrix is capableof being repetitively transformed from the first thermo-chemical stateto the second thermo-chemical state, and from the second thermo-chemicalstate to the first thermo-chemical state.
 27. The device of claim 23,where the thermo-chemically activated thermoplastic matrix is capable ofbeing transformed from the second thermo-chemical state to the firstthermo-chemical state by application of energy to the thermo-chemicallyactivated thermoplastic matrix from an outside source and is capable ofbeing transformed from the first thermo-chemical state to the secondthermo-chemical state by dissipation of energy from thethermo-chemically activated thermoplastic matrix to surrounding matter.28. The device of claim 23, wherein the device is capable of beingimplanted in a patient while the thermo-chemically activatedthermoplastic matrix is at the first thermo-chemical state, thethermo-chemically activated thermoplastic matrix is transformable to thesecond thermo-chemical state while the device is in the patient, and thedevice is configured to remain in the patient until thethermo-chemically activated thermoplastic matrix returns to the firstthermo-chemical state.
 29. The device of claim 23, further comprising alongitudinal axis, wherein the device is capable of radial expansioninto an expanded state, radial contraction into a contracted state,wherein the device is further capable of greater flexion about thelongitudinal axis while in the contracted state.
 30. The device of claim23, wherein the thermo-chemically activated thermoplastic matrix isbiocompatible and comprises a polymer selected from the group ofpolymers consisting of polylactic acid (PLA), poly ε-caprolactone (PCL),trimethylene carbonate (TMC), polyglycolic acid (PGA), poly l-lacticacid (PLLA), poly d-l-lactide (PDLLA), polyethylene terephthalate (PET),aliphatic polyesters, polyanhydrides, polyphosphazenes, polyorthoesters,poly(p-dioxane), polyaminoacids, pseudopolyaminoacids, erodablehydrogels, and natural polymers.
 31. The device of claim 30, wherein thethermo-chemically activated thermoplastic matrix further comprises ablend of polymers selected from the group consisting of polylactic acid(PLA), poly ε-caprolactone (PCL), trimethylene carbonate (TMC),polyglycolic acid (PGA), poly l-lactic acid (PLLA), poly d-l-lactide(PDLLA), polyethylene terephthalate (PET), aliphatic polyesters,polyanhydrides, polyphosphazenes, polyorthoesters, poly(p-dioxane),polyaminoacids, pseudopolyaminoacids, erodable hydrogels, and naturalpolymers, wherein the blend of polymers has a glass transitiontemperature selected to be near the body temperature of a patient. 32.The device of claim 30, wherein the thermo-chemically activatedthermoplastic matrix further comprises a bioactive material selected toenhance healing of the bone, wherein the bioactive material is selectedfrom the group consisting of hydroxyl apatite, tetracalcium phosphate,β-tricalcium phosphate, fluorapatite, magnesiumwhitlockite,β-whitlockite, apatite/wollastonite glass ceramic, calcium phosphateparticle reinforced polyethylene, bioactive glasses, bioactive glassceramics, polycrystalline glass ceramics, and polyethylene hydroxylapatite.
 33. A method for stabilizing a fractured bone, comprising:conforming a composite device to the bone, the composite devicecomprising a support structure connected to a thermo-chemicallyactivated thermoplastic matrix which is deformable at a firstthermo-chemical state and hard at a second thermo-chemical state, andtransforming the thermo-chemically activated thermoplastic matrix fromthe first thermo-chemical state to the second thermo-chemical state toharden the thermo-chemically activated thermoplastic matrix.
 34. Themethod of claim 33, wherein conforming the composite device to the bonefurther comprises radially expanding the composite device.
 35. Themethod of claim 33, wherein transforming the thermo-chemically activatedmatrix from the first thermo-chemical state to the secondthermo-chemical state further comprises allowing energy to dissipatefrom the thermo-chemically activated matrix.
 36. The method of claim 33,further comprising inserting the composite device into theintramedullary canal of the bone, wherein conforming the compositedevice to the bone comprises conforming the composite device to theintramedullary canal.
 37. The method of claim 36, wherein inserting thecomposite device into the intramedullary canal of the bone comprisesinserting the composite device along a path that is not parallel to theintramedullary canal of the bone.
 38. The method of claim 36, whereinthe support structure further comprises a series of telescoping nestablecomponents, wherein inserting the composite device into theintramedullary canal further comprises nesting the telescoping nestablecomponents within the intramedullary canal of the bone.
 39. The methodof claim 33, further comprising removing the composite device from theintramedullary canal of the bone after healing of the bone.
 40. A methodfor stabilizing a fractured bone, comprising: inserting athermo-chemically activated device into an intramedullary canal of thefractured bone; and conveying energy to or from the thermo-chemicallyactivated device to trigger transformation of the thermo-chemicallyactivated device from a first thermo-chemical state to a secondthermo-chemical state to increase rigidity of the thermo-chemicallyactivated device within the intramedullary canal.
 41. The method ofclaim 40, further comprising inserting the thermo-chemically activateddevice into the intramedullary canal along a pathway that is notparallel to the intramedullary canal.
 42. The method of claim 41,wherein the thermo-chemically activated device comprises a longitudinalaxis, wherein inserting the thermo-chemically activated device into theintramedullary canal further comprises flexing the thermo-chemicallyactivated device about the longitudinal axis.
 43. The method of claim40, further comprising radially expanding the thermo-chemicallyactivated device to conform to the shape of the intramedullary canalprior to transformation of the thermo-chemically activated device fromthe first thermo-chemical state to the second thermo-chemical state. 44.The method of claim 40, further comprising removing thethermo-chemically activated device from the intramedullary canal afterhealing of the bone.